This sentence would probably be a citation in APA style. Citations on research papers are very important since they give due credit to the original owner of the statement. Statements that don't have citations tells the readers that those statements are of the researcher/s alone which would be a problem for them if found out that it wasn't theirs to begin with. This would result to a work of plagiarism which is a grave sin in constructing research papers and is more equated with the act of stealing.
From reading the conclusion of the great gatsby, it seems that daisy would have mixed emotions. Firstly initially she would be happy that she can start her life again but in contradiction that her life she wanted to have was full of lies, sorrows and heartbreak.
It's a relative pronoun which introduces a relative clause.
